How to integrate existing systems into a SOA?

The question how to deal with existing systems often seems easy
to answer – at least in high level analyst presentations and glossy vendor brochures:
just build a wrapper and make it look like a service. This way the legacy system can
become an equal citizen in the world of SOA.

Of course, the reality that we face in our client projects is
usually quite different. Keeping a “wrapped” legacy system alive does not end the
maintenance burden that it has become over the years. And building the service wrapper
is often not possible in a non-intrusive way, which can result in a price point that
makes the approach not feasible; this approach can also have severe side effects that
create a risk that is not acceptable.

Successful SOA Integration requires a careful approach that weighs
the benefits of the available options against their cost and risks.